Siding Is the First Defense Against the Elements

Bird's-Eye View

Your first defense against the weather

Siding has both decorative and functional purposes, but some of the options come with a heavy environmental price tag. Choose a durable product that is low in toxicity and can be manufactured sustainably. The layers you don't see, such as housewraps, drainage mats, and insulated sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen.
panels, are just as important for durability and weatherization. Getting siding details right may be the most important step in creating a durable home — especially where roofs, decks, and porches make penetrations.

Wood

Paint lasts longer when the siding is vented.
Vertical strapping lets water drain down and air flow up. This allows the back of the siding to dry as fast as the front, keeping the wood stable and extending the life of the paint, siding, and sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen.
.

Local wood is a green choice

Wood siding, a first choice in some regions, is easy to work with, nontoxic, and completely biodegradable, depending on its finish. Some species are maintenance-free, but most need regular coats of paint. Back venting wood siding can make the paint last longer.

Stucco

TWO LAYERS OF FELT PAPER ARE BETTER THAN ONE. Over traditional stucco, the second sacrificial layer of felt paper bonds to the stucco and pulls away as the stucco dries. The gap between the two layers allows for drainage. To upgrade, add a mesh drainage mat.

Stucco and synthetic stucco

are extremely durable wall finish materials, as long as they are installed with details to handle moisture intrusion. Exterior insulation and finish system (EIFS), also called synthetic stucco, is a modern alternative to stucco that combines a polymer claddingMaterials used on the roof and walls to enclose a house, providing protection against weather.
with a substrate of polystyrene insulation.

Brick

Brick veneer needs a drainage space. Brick absorbs a lot of water during rain, and some of that water dries to the inside when the sun comes out (the sun drives water farther into the wall assembly). If that water can't escape, the walls can rot. Foam sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen.
is a great choice behind brick.

Insects are not a concern, but moisture is

Low-maintenance, highly durable brick veneer is also fire- and insect-resistant. As with stucco, brick veneer needs to be installed with details that are designed to address moisture intrusion.

Stone

Make room for drainage Applying two layers of #30 felt creates a drainage plane between them. Wire lath over the felt paper allows the mortar to adhere to the wall.

Stone and synthetic stone

Facing a wood-framed building with stone or synthetic stone is a good way to get the look of traditional masonry at a lower cost than traditional construction methods. Both materials are fire- and insect-resistant, need very little maintenance, and are among the most durable wall claddings available — as long as flashing and moisture details are well thought out and executed.

Fiber cement

Fiber cement has many maintenance benefits. Fiber
cement is impervious to damage from rot and insects, it holds paint welland it won’t burn. It won’t expand or contract with temperature and moisture fluctuations.

Durable, but the details of its manufacture are controversial

Fiber-cement (cementitious) siding has some real durability advantages but isn’t the easiest type to install. Two of fiber cement's ingredients raise a few environmental concerns — Portland cement, due to the energy required by its production, and wood fiber, due to sourcing and transportation costs — but almost every home already includes them. Some manufacturers are using alternative components that make their products greener.

Vinyl

Vinyl siding makes sense sometimes Vinyl siding is inherently back-vented, so it handles rain well. In coastal spots where salt air and sideways-driven rain eat up siding, vinyl is a low-maintenance and affordable choice.

Vinyl: Loved and hated

Homeowners love it for its low maintenance requirements and modest installation cost, and vinyl siding performs extremely well from a moisture-management perspective. But it has the same environmental drawbacks as other products made from polyvinyl chloride (PVC).

DIVE DEEPER

OTHER CONSIDERATIONS

Plan for wetness
Getting siding details right may be the most important step in creating a durable home. All siding types leak, but leaks may also occur where siding abuts other building materials, such as roofing or a masonry chimney. Potential trouble areas include any penetration through a wall, such as at windows, doors, decks, porches or additions. The installation of the layers you don't see behind the siding, such as housewraps, drainage mats, and insulated sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen.
panels, are just as important for durability and weatherization.

DRAWING LIBRARY CONSTRUCTION DETAILS

GREEN POINTS

LEED–H MR2.2 (Materials & Resources) offers 1/2 point for environmentally preferable siding, including FSCNonprofit organization that promotes forestry practices that are sustainable from environmental and social standpoints; FSC certification on a wood product is an indicator that the wood came from a well-managed forest., salvaged, and recycled-content options; 1/2 point more if it is locally sourced.

NGBSNational Green Building Standard Based on the NAHB Model Green Home Building Guidelines and passed through ANSI. This standard can be applied to both new homes, remodeling projects, and additions.
Under Chapter 6, "Resource Efficiency": weather-resistive barrier (WRB mandatory (602.9); up to 6 points for insect-resistant materials (602.8); up to 2 points for siding that does not require site-applied finish (601.7); up to 8 points if siding contributes as a bio-based component (606.1).

ABOUT SIDING

Durable, low-maintenance siding is best

Durable siding requiring little maintenance is the appropriate choice for a green home.

Siding is an important architectural feature. There are half a dozen major families of siding, and many variations within those categories. Some are strong regional favorites, either because they are well suited to the climate or because they have a long local history (usually both).

In addition to durability, criteria for choosing siding include cost, maintenance requirements, ease of installation, and environmental impact.

ABOUT RAINSCREENS

Even the best claddingMaterials used on the roof and walls to enclose a house, providing protection against weather.
will fail if it is installed improperly. The performance of all of the materials listed above depends on the quality of installation, including the water-resistive barrierSometimes also called the weather-resistive barrier, this layer of any wall assembly is the material interior to the wall cladding that forms a secondary drainage plane for liquid water that makes it past the cladding. This layer can be building paper, housewrap, or even a fluid-applied material., flashing, and back-venting (or rainscreen) details that allow the siding to dry properly from the back. (For more information on WRBs, see All About Water-Resistive Barriers.)

In most cases, the investment in a rainscreen siding installation pays dividends in paint longevity and siding durability.

VinylCommon term for polyvinyl chloride (PVC). In chemistry, vinyl refers to a carbon-and-hydrogen group (H2C=CH–) that attaches to another functional group, such as chlorine (vinyl chloride) or acetate (vinyl acetate). siding is inherently well ventilated and always has air behind it. Brick veneer, if installed according to code requirements, always includes a ventilated air space between it and the sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen.
. Neither vinyl siding nor masonry veneers needs a rainscreen.

Siding without a rainscreen
Other types of siding — wood clapboard, cedar shingles, fiber-cement — are often fastened tight to the sheathing with no intervening air space. Such installations can perform well, especially in a dry climate or on a wall that is protected by a wide roof overhang. But such installations are less forgiving than rainscreen installations, and often experience premature paint failure. If one or two things go wrong, walls without a rainscreen can trap moisture and begin to rot. For more information on what can go wrong if a wall is poorly detailed, see All About Wall Rot.

To create a rainscreen, first install a layer of asphalt felt or housewrap over the sheathing. The wrap must be carefully integrated with window and door flashing. For horizontal siding like wood clapboards or fiber-cement, an air space can be created by installing vertical strapping over each stud. A variety of materials can be used for strapping, including 1x3 lumber, rips of 1/4-inch plywood, or plastic battens.

For panel siding, cedar shingles, or stucco, create an air space with a three-dimensional plastic mat (for example, Cedar Breather) or a plastic dimple sheet.

Anonymous,
Stucco has no appreciable R-value. Moreover, an air space can add to the R-value of the wall assembly -- about R-1 additional.

1.
Sep 24, 2010 1:58 PM ET

Does air space lower R- value? by Anonymous

"For panel siding, cedar shingles, or stucco, create an air space with a three-dimensional plastic mat (for example, Cedar Breather) or a plastic dimple sheet"
If we create an air space between stucco and sheathing wouldn't it lower the R - value of stucco?